How to Get Stop Light Signal for a Brake Controller on a 2021 Volvo XC90

Updated 04/13/2026 | Published 10/05/2025

Question:

Hi, I have a Prodigy P3 that Im trying to wire into our 2021 Volvo XC90. Which wire do I get the brake signal from the brake pedal to connect to red on the universal wiring harness? Im not finding one that provides 0V and then 12V when activated. The P3 is a recommended controller for the vehicle.

asked by: Joel

Expert Reply:

Hey Joel!

I did some digging, but I wasn't able to locate the exact wire you're trying to find.

Every once in a while, we come across situations like this where people have a hard time finding the stop light circuit under the driver's side dash. When this is truly the case, the best course of action is to install the Roadmaster Universal Stop Light Switch Kit # RM-751000 which is just an alternative way to easily gain access to a signal that only gets hot when the brake pedal is pressed.

Aside from the universal stop light switch, the only other way I know how to get that signal is to pull from the 3rd brake light on your 2021 Volvo XC90.

Which way would you rather lean towards?

expert reply by: Jon G

Jon G.

10/30/2025

Hey Joel, what route did you end up taking to get the brake signal for your Prodigy P3 on the Volvo XC90? Your update could make it easier for others trying to wire their controller the same way.

Joel

12/10/2025

@JonG, I hadn't had time to get back to this. There are three wires going to something on the side of the pedal and two going to the front. I couldn't get a 12v signal from the three on the side and am having trouble getting a read on the two in the front. If I can't get a signal there I'd probably use the stop light switch kit over running a wire and tying into the 3rd brake light.